1. Field of the Invention
The present invention relates to air cycle machines, as used in high performance pressurized aircraft for control of the interior environment of the aircraft. More specifically, the present invention comprises a specially formed insert or liner for installation in the turbine section of the air cycle machine, and a method of modifying the turbine section for installation of the insert and installing the liner or insert.
2. Description of the Related Art
Air cycle machines are installed in high performance pressurized aircraft to condition the cabin air and control the environment (i.e., temperature and humidity) within the passenger cabin and crew compartment of the aircraft. The housing sections of these machines are formed of magnesium, used primarily due to its strength to weight ratio and other beneficial properties. However, the magnesium castings are prone to cracking, particularly in the turbine section of the machine due to the temperature differential across the wall of the turbine air passage.
Even though the air has passed through a heat exchanger prior to entering the turbine section, the air remains at a relatively high temperature in the turbine before exiting the turbine through a series of expansion nozzles where the air expands and cools. The cooled and expanded air enters an expansion chamber directly behind the turbine air passage, with the relative temperature differences on each side of the wall between the expansion chamber and the turbine air passage resulting in considerable thermal stress on the wall. This leads to cracks forming in the turbine air passage wall over a period of time and operational heat cycles of the air cycle machine. The interior surface of the air passage wall is also eroded over time due to fine particulates carried in the air as it passes through the machine, particularly during ground operation.
Heretofore, the means of repairing such a damaged air cycle machine was to replace the damaged component, i.e., the turbine housing. Obviously this is a costly operation, as the housing is a complex cast and machined component. The labor involved is considerable as well, as the turbine housing is sandwiched between the compressor housing and the fan containment housing and the rotor shaft passes through the various housings as well. Thus, essentially the entire air cycle machine must be disassembled in order to remove the defective turbine housing, and reassembled with a new or reconditioned turbine housing.
Various devices and methods have been developed in the past for repairing and/or insulating components affected by heat within turbines and other compression machines. For example, German Patent Publication No. 3,921,423 published on Jan. 4, 1990 describes (according to the drawings and English abstract) a method for reducing weld defects in the welding of a compression unit to a housing, comprising a double weld in which the second weld corrects any defects from the first weld.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, an air cycle machine repair insert and method of repair solving the aforementioned problems is desired.